The tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymers, commercially known as PFA, are melt-processable polymers characterized by a high melting point, high thermal stability, chemical inertness and low dielectric constant, as well as good mechanical properties at room and elevated temperature. Generally, a commercial PFA polymer has a melting point of approximately 305° C. and a continuous use temperature of 260° C., wherein the parameter of continuous use temperature indicates the highest operating temperature the polymer can continuously withstand. Therefore, PFA polymers are widely used in industrial applications which require a high operating temperature and possibly a chemically aggressive environment, such as transportation pipes and heat exchanger in chemical process industry, communication cables for some extreme environments, and flexible risers operating at high temperatures.
Nevertheless, in many real-world industry applications in the oil and gas field, the need has been felt to have melt-processable polymer materials having a continuous use temperature beyond 260° C., to withstand extremely high operating temperatures encountered in construction work and the like. For instance, with deep drilling, a data communication cable can be exposed to temperatures of 280° C. or higher in a downhole well.
Recently, to address this limitation, related patent applications US 2012/0034406 (E. I. DU PONT DE NEMOURS AND COMPANY) Feb. 9, 2012, US 2012/0035326 (E. I. DU PONT DE NEMOURS AND COMPANY) Feb. 9, 2012, WO 2012/019070 (E.I. DUPONT DE NEMOURS AND COMPANY) Sep. 2, 2012 and US 2012/0031607 (E. I. DU PONT DE NEMOURS AND COMPANY) Feb. 9, 2012, proposed a process to modify the existing PFA polymer, by incorporating a melt flowable polytetrafluoroethylene (PTFE) into the original PFA polymer and thereafter heat treating the resultant composition at a temperature of at least 280° C., wherein the melt flowable PTFE is a low molecular weight polymer (LMW PTFE). According to the afore recited applications, incorporation of LMW PTFE in the original PFA polymer is necessary, for improving the latter's integrity during heat treatment exposure and enables the resultant composition to exhibit improved physical properties such as flex-life value and tensile strength, a desirably low MFI (melt flowing index), and a relatively high continuous use temperature (i.e. greater than 260° C.).
Nevertheless, the approach of the afore-recited applications requires: 1) the addition of selected LMW PTFE into the original co-polymer and 2) a fine-tune of the proportions between PFA and LMW PTFE for producing a desired result, which complicated the polymer modification process.
There is thus a need for a continuous search for new, simple approaches to modify the existing PFA polymer in order to improve its overall performance at room and elevated temperatures, in particular the properties like flex-life, MFI, tensile creep, barrier properties, and continuous use temperature.
WO 2014/086694 (SOLVAY SPECIALTY POLYMERS ITALY, S.P.A.) Dec. 6, 2014, discloses a method for heat treating certain melt-processable fluoropolymers, in the absence of any PTFE. Nevertheless, this document is barely silent on the end group content of the melt-processable fluoropolymers thereby submitted to heat treatment.